Departament de Psiquiatria I Psicobiologia Clinica, Universitat de Barcelona, Catalonia, Spain.
Cortex. 2012 Oct;48(9):1187-96. doi: 10.1016/j.cortex.2011.07.006. Epub 2011 Aug 5.
Brain regions simultaneously activated during any cognitive process are functionally connected, forming large-scale networks. These functional networks can be examined during active conditions [i.e., task-functional magnetic resonance imaging (fMRI)] and also in passive states (resting-fMRI), where the default mode network (DMN) is the most widely investigated system. The role of the DMN remains unclear, although it is known to be responsible for the shift between resting and focused attention processing. There is also some evidence for its malleability in relation to previous experience. Here we investigated brain connectivity patterns in 16 healthy young subjects by using an n-back task with increasing levels of memory load within the fMRI context. Prior to this working memory (WM) task, participants were trained outside fMRI with a shortened test version. Immediately after, they underwent a resting-state fMRI acquisition followed by the full fMRI n-back test. We observed that the degree of intrinsic correlation within DMN and WM networks was maximal during the most demanding n-back condition (3-back). Furthermore, individuals showing a stronger negative correlation between the two networks under both conditions exhibited better behavioural performance. Interestingly, and despite the fact that we considered eight different resting-state fMRI networks previously identified in humans, only the connectivity within the posteromedial parts of the DMN (precuneus) prior to the fMRI n-back task predicted WM execution. Our results using a data-driven probabilistic approach for fMRI analysis provide the first evidence of a direct relationship between behavioural performance and the degree of negative correlation between the DMN and WM networks. They further suggest that in the context of expectancy for an imminent cognitive challenge, higher resting-state activity in the posteromedial parietal cortex may be related to increased attentional preparatory resources.
在任何认知过程中同时激活的大脑区域在功能上是相连的，形成大规模的网络。这些功能网络可以在活跃状态下进行检查（即任务功能磁共振成像（fMRI）），也可以在被动状态下进行检查（静息 fMRI），其中默认模式网络（DMN）是研究最广泛的系统。DMN 的作用尚不清楚，尽管已知它负责从静息状态到专注状态处理的转变。也有一些证据表明，它与之前的经验有关，可以灵活变化。在这里，我们通过在 fMRI 环境中使用具有不同记忆负荷水平的 n-back 任务，研究了 16 名健康年轻受试者的大脑连接模式。在进行这项工作记忆（WM）任务之前，参与者在 fMRI 之外接受了简短测试版本的训练。之后，他们立即进行静息状态 fMRI 采集，然后进行完整的 fMRI n-back 测试。我们观察到，在最具挑战性的 n-back 条件（3-back）下，DMN 和 WM 网络内的固有相关性程度最大。此外，在两种情况下，两个网络之间的负相关程度较强的个体表现出更好的行为表现。有趣的是，尽管我们考虑了以前在人类中识别的八个不同的静息状态 fMRI 网络，但仅在 fMRI n-back 任务之前，DMN 后内侧部分（楔前叶）内的连接性预测 WM 执行。我们使用 fMRI 分析的基于数据驱动的概率方法的结果提供了行为表现与 DMN 和 WM 网络之间负相关程度之间直接关系的第一个证据。它们进一步表明，在预期即将发生认知挑战的情况下，后内侧顶叶皮层的静息状态活动增加可能与注意力预备资源的增加有关。
